Apparatus for developing electrostatic charge images



Oct. 7, 1969 w. SIMM 3,470,850

APPARATUS FOR DEVELOPING ELECTROSTATIC CHARGE IMAGES Filed Dec. 6. 1967INVENTOR.

WALTER S/MM United States Patent 3,470,850 APPARATUS FOR DEVELOPINGELECTROSTATIC CHARGE IMAGES Walter Simm, Leverkusen, Germany, assignorto Agfa- Gevaert Aktiengesellschaft, Leverkusen, Germany, a corporationof Germany Filed Dec. 6, 1967, Ser. No. 688,434 Int. Cl. Bb 5/02; B05c5/02; G03g 13/10 US. Cl. 118637 5 Claims ABSTRACT OF THE DISCLOSURE Aset of charged rapidly rotating rollers providing spaces about 0.5 to 5mm. wide restrict flow of aerosol dye particles used to developelectrostatic image, but constitute effective maintenance-free auxiliarydeveloping electrode. Rollers are rotated in direction that helpsparticles move through the spaces.

This invention relates to an apparatus to be used for developingelectrostatic images with electrostatically charged dye aerosols. Theapparatus consists of a conductive support for the recording materialcontaining the electrostatic image, an electrostatic atomizationelectrode, and a development electrode arranged between the recordingmaterial and atomization electrode and close to the recording surface ofthe recording material.

It is already known that one may use grid-shaped development electrodesin the above-described arrangement and that the charged dye aerosolwhich is produced from an atomization electrode may be sprayed throughthis grid onto the surface on which development is to take place. Thegrid electrode can be used to control the deposition of the aerosol onthe recording material by trapping excess developer dye. An apparatus ofthis type is described in German Patent No. 1,172,955.

One disadvantage which arises out of the use of a grid electrode is thatthe meshes of the grid soon become partly or completely blocked bydeveloper dye unless they are frequently cleaned. If the grid were notcleaned, it would very soon become useless. However, cleaning entailsconsiderable expense in taking time and requiring equipment, andcleaning agents, especially in the case of automatic developingequipment.

The object of the present invention is to replace the grid electrode bya different type of development electrode which is easier to clean. Anychanges which are made to the external form of the grid electrode shouldnot affect the desired electrical properties and the particularadvantages of the grid. These include, for example, the function of thegrid whereby it serves as counterelectrode for the charge image, anauxiliary field being produced which controls the deposition of theaerosol in imagewise fashion. Another advantage of the grid is itssimultaneous use as a counterelectrode for the atomization electrode,the powerful electrical atomization field produced on one side of thegrid being separated from the relatively Weak image field on the otherside of the grid.

According to the present invention, this problem is solved by using, inthe development of charge images with electrically charged dye aerosols,an apparatus which comprises a conductive support for the recordingmaterial having the electrostatic image, an electrostatic atomizationelectrode, and a development electrode arranged between the recordingmaterial and atomization electrode, close to the recording surface ofthe material, and which is characterised in that the developmentelectrode comprises a plurality of electrically conductive rotatingrollers which are arranged with their axes parallel and in one planewhich is parallel to the surface of the recording material.

This development electrode which takes a completely different form fromthe grid electrode previously in use surprisingly fulfils allrequirements. It is eminently suitable both for developing line imagesand for developing half-tone images, and has moreover the advantage thatit can be cleaned in a simple manner while it is in continuousoperation.

The rollers are rotatably mounted and when in operation they rotate athigh speed about their longitudinal axes. The rollers can be in pairs,those of a pair preferably rotating in an opposite sense to each other.The disstance between the rollers is so small that the electrical fieldof the atomization electrode on one side of the roller arrangement issufficiently separated from the image area on the other side of thearrangement. The rotation of the roller causes part of the dye aerosolwhich is sprayed from one side through the atomization electrode to becarried by the layers of air rotating with the rollers, and thus enterthe region of the electrostatic image field over the surface of therecording material, where deposition takes place and hence the image isdeveloped. The remainder of the dye is deposited on the surface of therollers and can be removed by a suitable stripper, either continuouslyor intermittently. The imagewise deposition of aerosol is controlled bythe fact that the rollers and the surface on which the image is to beformed are connected to each other through a source of direct voltagewhich yields an adjustable voltage up to the maximum voltage of theimage charge.

A simple embodiment of the development apparatus is illustrated inFIGURES l and 2 of the accompanying drawings which are verticalsectional views taken transversely and longitudinally of such anapparatus. A recording material 1 which carries an electrostatic chargeimage which is to be developed, e.g. an electrophotographic layer, issituated on a conductive, grounded support 2. Two metal rollers 3 and 4which are rotatably mounted on a shaft in bearings 5 and 6 and which caneach be rotated by drive motors 7 are arranged 0.5 to 3 mm. from therecording material 1. The motors are designed for very high speeds ofrotation, e.g. 15,000 revs./ min. The length of the rollers depends onthe size of the image, their diameter preferably being in the region of10 to 50 mm. The distance between the rollers is adjusted to 0.5 to 5mm.

The support 2 with recording material 1 is slidably arranged on gliderails 8 and 9 to he slid in the directions of the arrows. It isnecessary that one be able to displace this assembly during development,since otherwise the image would be developed only in an areacorresponding to the space between the upper portions of the rollers.

An atomization electrode 10 which is in the form of a rotating disc theedge of which is wetted with dye solution by immersion in a dyecontainer 11 is situated below the pair of rollers. Electrode 10 isrelated by means of a motor 12 and a shaft 13 part of the length ofwhich, at least, is of insulating material. The high voltage requiredfor atomization of the dye liquid, which voltage is taken from a highvoltage source 14, is applied to the disc 10.

Instead of the disc electrode 10, a ring electrode according to Germanpatent application A 51,884 may be used (certified copy in file of Ser.No. 619,415 filed Feb. 28, 1967). Other suitable types of electrodes aredescribed in German patent specifications Nos. 1,187,134 and 1,202,-639. The electrode 10 is surrounded by a housing 15 made of electricallyinsulating material, which is open at the top and is largely covered bythe pair of rollers 3 and 4. In this housing, a gas of high electricalpotential, e.g. the compound CF Cl can be supplied to the atomizationelectrode from a pipe connection 19, the atomization efficiency of theelectrode being thereby improved in known manner.

The rollers 3 and 4 are connected via the bearings to a rotatingstructure is connected to rotate the rollers in the voltage source 16which supplies an adjustable voltage of to 5000 v. Strippers 17 and 18contact the outsides of the rollers to remove the dye that is depositedon the surface of the rollers and hence prevent the building up of suchdeposits.

In principle, the pair of rollers could-be replaced by a single roller,but this significantly reduces the efliciency of transfer of dye to theimage support.

To shorten the development time and to make possible the developmentof'large image surfaces, apparatuses may be used which comprise severalelectrode arrangements according to FIGURES 1 and 2.

By using the apparatus according to the invention, development of chargeimages with particles of dry dye, which have been produced e.g. asdescribed in German patent application A 49,273 (certified copy on filein US. application Ser. No. 549,808 filed May 13, 1966) can be carriedout continuously. Additional measures for cleaning the developmentelectrodes are then no longer necessary.

I claim:

1. In an apparatus for developing electrostatic images with electricallycharged aerosol dye particles and having guide structure for guidinginto developing position a member carrying the electrostatic image to bedeveloped, an electrically charged development electrode opposing theimage, and atomizing elements to atomize particles of dye solution intothe space beyond the auxiliary electrode for migration through thatelectrode to the image, the improvement according to which thedevelopment electrode is in the form of a set of spaced generallyparallel rollers confining the movement of the atomized developerparticles to spaces about 0.5 to millimeters wide, and

- direction thathelps carry the particles through the spaces.

2. The combination of claim 1 in which the rollers are arranged in pairswith the spaces between the two rollers of each pair, and the rotatingstructure is connected to rotate the two rollers of each pair' inopposite directions at very high speeds. j' m 3. Thecornbiria'tion'ofclaim 1 in which each roller has a stripper thatscrapes deposits from its surface as it rotates. i r p 4. Thecombination of claim 1 in which a housing confines the atomizingelements as well as the'space below each roller.

5. Theicornbination of claim 4 in which the housing is provided with aninlet for receiving a blanketing gas.

lieferences Cited STATES PATENTS UNITED 2,777,784 7 1/1957 Miller 117-932,928,575 3/1960 Carlson 222-193 3,140,199 7/ 1964 York 1 18-6373,169,887 2/1965 York 118-637 3,171,600 3/1965 Eckey 239-220 3,256,8556/1966 Oliphant 118-637 3,323,933 6/1967 Barford et a1. 117-17 3,355,28811/1967 Matkan 117-175 XR 3,367,791 2/1968 Lein 118-637 XR PETERFELDMAN, Primary Examiner v US. 01. X.R. 117-37, 93.4; 11s 300, 626;239-420

